Acrylamide has many applications, such as flocculating agents, petroleum recovering agents, paper strength enhancers in the paper producing industry, and thickeners for papermaking, and is a useful substance as a raw material for polymers.
Among industrial processes for acrylamide production, used long time ago is a sulfuric acid hydrolysis process which consists of the step of heating acrylonitrile together with sulfuric acid and water to obtain an aqueous solution of acrylamide sulfate salts. This process has then been replaced with a copper-catalyzed process in which acrylonitrile is reacted with water in the presence of a copper catalyst (for example, metal copper, reduced copper, Raney copper, or the like) to obtain an aqueous solution of acrylamide. In addition, in recent years, as a production process with fewer by-products, industrial production based on a biocatalyst method is also carried out as a biocatalyst method for obtaining an aqueous solution of acrylamide by using a biocatalyst such as nitrile hydratase derived from microorganisms (for example, Patent Documents 1 to 4).
As in the case of many unsaturated monomers, acrylamide is easy to polymerize by the action of light or heat and also has a property of very easily polymerizing particularly upon contact with the surface of iron, so that an aqueous solution of acrylamide has been difficult to stably handle since the polymerization of acrylamide easily occurs during each step of its production or during its preservation.
A method of using various stabilizers has been proposed as a method for stabilization by suppressing polymerization of acrylamide. Examples of the stabilizers include thiourea, ammonium rhodanide, nitrobenzol (Patent Document 5), ferron (Patent Document 6), furil dioxime (Patent Document 7), cyanide complex compound of chromium (Patent Document 8), p-nitrosodiphenyl hydroxyamine (Patent Document 9), and so on. Those stabilizers are used for preventing polymerization during a process of producing acrylamide or for stabilization of an aqueous solution of acrylamide.